During medical procedures which utilize catheters and guide wires, a distal portion of the catheter or guide wire can sometimes accidentally detach from the rest of the article and be left within the patient. This fragment may then travel, e.g., within the vascular system until it comes to rest either within a vein or artery, usually at a branching point, or in a body cavity, such as the heart. The results of leaving these foreign bodies within a patient can be quite harmful, and include septicemia, multiple pulmonary emboli, perforation, and even sudden death.
In the past, foreign articles were often left in place despite these grave risks because the procedural options for removal were highly traumatic. The risks associated with open heart surgery to remove items lodged in the heart, for example, may well outweigh the problems inherent in allowing the article to remain.
Safer techniques were then developed to remove foreign objects from the body. These techniques use a grasping mechanism carried within a catheter to grip the foreign object and retract it to a more accessible location or even out of the patient through the catheter's site of entry.
Three basic configurations of grasping mechanisms are most commonly employed: a modified urological stone basket, rigid forceps, and a snare comprising a loop of wire extending from the forward end of a catheter. The stone basket technique utilizes an assembly of a plurality of wires within a sheath, the assembly being threaded through a catheter. The wires are all joined at their distal end and, when the wires protrude beyond the tip of the sheath, the wires become spaced away from one another to define a wire "basket." The basket is closed by retracting the wires within the sheath and opened by advancing the wires through the tip of the sheath
Forceps used in these types of operations are much like those used in bronchoscopic procedures and comprise a pair of rigid fingers which may be urged toward one another to pinch the object therebetween. Use of these devices is limited almost exclusively to items lodged in relatively large cavities such as the right atrium or venacava. Although this instrument has one major advantage in that it may grasp the item to be retrieved at any point, the rigidity of the instrument limits maneuverability and creates a risk of perforation of the walls of the cavity or vessel.
The third grasping mechanism, the snare, is probably the most widely used. Commonly, a long wire is folded in half and the folded end is passed through a catheter from its proximal end to its distal end adjacent the article to be retrieved. Once the folded end portion of the wire extends beyond the distal tip of the catheter, one of the two proximal ends of the wire is retracted to induce formation of a loop in the distal end adjacent the end of the catheter. A suitable loop usually will not form without such relative movement of the two strands of the folded wire. A permanent bend or crease is necessarily formed in the wire when it is folded. When it protrudes beyond the distal tip of the catheter, the fold remains and inhibits the wire from expanding into a loop in the absence of relative axial movement of one wire strand with respect to the other.
Once a loop has been formed, the foreign body fragment may be ensnared within the loop. Repeated passes at a free end of the fragment frequently must be attempted before the loop passes over the fragment. Successful engagement is indicated by movement of the fragment, usually viewed with fluoroscopic equipment Once engagement has been accomplished, the foreign article is pinned between the loop and the distal tip of the catheter. This may be performed by either (1) retracting one strand of the folded wire, making the loop smaller, or (2) relative movement between the entire wire and the catheter, usually by advancing the catheter over the wire until it closely contacts the ensnared body. The entire system, including the item to be retrieved, may then be retracted while engagement of the item against the catheter tip is maintained.
The snare technique is often rather difficult to utilize successfully, however. The wires used are commonly standard guide wires formed of stainless steel or like metals, which have a tendency to kink, particularly if smaller diameter wires are used. Such thin wires are necessary in many applications, however, because a double thickness of the wire must be passed through the inner lumen of the catheter and the diameter of the catheter is limited by the size of the vessels through which it is guided. This requirement of small diameter wires decreases stiffness, and hence controllable maneuverability, of the wire. Lower maneuverability limits utility in accessing remotely located fragments and makes it more difficult to control the loop when attempting to pass the loop over a portion of the foreign body fragment.
Snares known in the art suffer another deficiency as well. The loop that is formed at the tip necessarily lies in a plane parallel to the catheter. Unless a free end of the foreign body fragment happens to be substantially perpendicular to the plane of the loop, slipping the loop over the fragment may require many passes at the item. If this is unsuccessful, the physician ma have to resort to prodding the item to reorient the free end into a more acceptable position. While this may work in larger cavities where there is room to maneuver, the position of the loop may be problematic if the fragment has traveled to a remote site within a vessel where movement is much more limited.
Attempts have been made to avoid these problems. The basket mentioned above has been suggested as superior in some instances because the multiplicity of wires with slightly varying orientations ma increase the chance of grabbing the fragment. At least one researcher has attempted to solve this by providing a loop which extends to the side of a central, straight guide wire. (See Bloomfield, "The Non-Surgical Retrieval Of Intracardiac Foreign Bodies An International Survey," Catheterization And Cardiovascular Diagnosis, 4 (1978), 1-14.) This instrument incorporates a standard guide wire and catheter with a loose nylon thread carried on one side of the catheter. The thread is attached at two points along the exterior of the catheter, forming a loop which hangs to the side of the apparatus. This device has rather limited use due to the lack of control over the slack nylon loop and the inability to cinch the loop to tightly grip the fragment, which can severely hamper retraction. Also, use in more confined locations is limited because the catheter must be able to pass alongside an end of the article before the loop may be slipped over the end.